Pelvic Discontinuity Associated With Total Hip Arthroplasty

Evaluation and Management

Matthew P. Abdel, MD; Robert T. Trousdale, MD; Daniel J. Berry, MD

Disclosures

J Am Acad Orthop Surg. 2017;25(5):330-338. 

In This Article

Management

The three factors that influence the likelihood of successful management of pelvic discontinuity are the remaining host bone stock, the potential for biologic ingrowth, and the potential for healing. As such, the main goals of reconstruction are obtaining rigid and durable (preferably noncemented) fixation of the acetabular component to the pelvis, and creating a unitized hemipelvis, either by healing across the discontinuity or by healing of the pelvis to the superior and inferior aspects of the acetabular construct.

The approach for any revision surgery is selected based on surgeon preference; however, the posterolateral approach is most often used for the techniques discussed later because it provides excellent exposure of the acetabulum (including the posterior column and ilium) and the femur. The patient is placed in the lateral decubitus position, ensuring that the pelvis is perpendicular to the surgical table. This allows identification of anatomic landmarks and orientation of the acetabular component. The sciatic nerve should be identified and protected throughout the procedure. The sciatic nerve may be densely scarred to the area of the discontinuity and, thus, difficult to identify. Typically, the nerve can be identified distally in the adipose tissue deep to the gluteus maximus tendon, traced proximally, and freed from adhesions to the posterior column if necessary. Hip flexion and knee extension place undue tension on the sciatic nerve. Thus, it is preferable to place the hip in extension and the knee in flexion.

Trochanteric, extended trochanteric, Wagner, or transfemoral osteotomy may be performed if necessary to achieve additional exposure.[15] The decision to perform osteotomy is often based on several factors, including the ability to achieve intraoperative mobilization of the femur, the type of femoral component in situ and whether it needs to be revised, the status of the greater trochanter, the type and location of in situ acetabular components, and the quantity and quality of remaining acetabular bone. When the femoral component is being revised, we prefer to use an extended trochanteric osteotomy that is 12 to 14 cm long (Figure 3). When a custom triflange implant is used, more extensive exposure of the ilium, ischium, and pubis is required. The exposure posteriorly for the ischium must be done carefully because of the risk for sciatic nerve palsy, particularly of the peroneal branch. Furthermore, achieving extensive exposure of the ilium without damaging the superior gluteal nerve is challenging. A trochanteric osteotomy mitigates this risk, but it may complicate healing in patients with proximal femoral bone deficiency. After optimal exposure, care must be taken to remove well-fixed noncemented and cemented acetabular implants while minimizing bone loss. Curved, size-specific gouges are especially helpful in implant removal.

Figure 3.

Intraoperative photograph depicting an extended trochanteric osteotomy completed 12 to 14 cm from the tip of the greater trochanter to remove a long cemented femoral stem. This osteotomy facilitated acetabular exposure and subsequent reconstruction.

After implant removal and achievement of adequate acetabular visualization, curets are used to remove the fibrous membrane from the acetabular floor. Bone loss is assessed. A picador is used to stress the inferior aspect of the ischium. Any motion between the superior and inferior aspects of the acetabulum indicates a pelvic discontinuity.

Hemispheric Acetabular Component and Open Reduction and Internal Fixation With Plating

Posterior column compression plating is a good treatment option for acute pelvic discontinuity and in some instances of chronic pelvic discontinuity in patients with relatively good bone stock (Figures 4 and 5). For instance, when pelvic discontinuity occurs during insertion of an acetabular component in primary THA, a noncemented hemispheric acetabular component with plating is a reasonable treatment option. The goal of plating is to stabilize the discontinuity via compression, thereby promoting fracture healing.

Figure 4.

Illustration depicting a hemispheric acetabular component with posterior column compression plating for the management of an acute pelvic discontinuity with adequate host bone quality and quantity for healing. (Reproduced with permission from the Mayo Foundation for Medical Education and Research, Rochester, MN.)

Figure 5.

AP radiograph of the pelvis in the patient shown in Figure 2 after posterior column compression plating and placement of a hemispheric acetabular component.

Healing potential is dependent on the patient's biology and the intraoperative characteristics of the discontinuity. Autologous iliac crest bone grafting may increase the likelihood of discontinuity healing. An important goal with this form of reconstruction is placement of a hemispheric acetabular component with rigid fixation to foster biologic ingrowth. At least 50% of the cup should be in contact with the host bone, and at least three or four screws should be used to fix the cup to the host bone. If possible, additional screws should be placed through the cup into the ischium or superior pubic ramus to prevent the cup from failing in abduction.[16] Disadvantages of any large surgical exposure with increased soft-tissue dissection include increased risk of infection and decreased potential for biologic healing.[17]

Cup-cage Construct

Recent innovations in highly porous acetabular components offer enhanced biologic and mechanical properties.[7,18] A high coefficient of friction against bone is one benefit of highly porous acetabular implants.[18] Furthermore, the low stiffness of these implants may promote physiologic load transfer while minimizing stress shielding.[18] As such, highly porous metal acetabular components are particularly effective in managing pelvic discontinuity, for which bone quality and quantity, including bones previously managed with pelvic irradiation, are often compromised.[7]

The cup-cage technique involves placement of a highly porous jumbo acetabular component on the remaining host bone. A jumbo cup is one that measures ≥62 mm in women and ≥66 mm in men.[19,20] If needed, highly porous metal augments can be added to fill the remaining bone defects. A cage is placed over the acetabular component, spanning the discontinuity from the ilium to the ischium. The cage can be secured inferiorly with screws or with a flange in the ischium (Figures 6 and 7). The cup and cage are unitized with a screw that is placed through the cage and extends into the cup and host bone.

Figure 6.

Illustration of a cup-cage construct with supplemental screws placed superiorly and inferiorly, as well as a cage spanning the discontinuity from the ilium to the ischium. The cage can be secured inferiorly with screws or through a flange in the ischium. (Reproduced with permission from the Mayo Foundation for Medical Education and Research, Rochester, MN.)

Figure 7.

Postoperative AP radiograph of the pelvis in a 51-year-old woman with a pathologic pelvic discontinuity managed with a cup-cage construct with supplemental screws placed superiorly and inferiorly as well as a highly porous augment. To accommodate the limited ischial bone and minimize the risk of sciatic nerve injury, multiple inferior screws were inserted superiorly through the porous cup and halfcage construct.

In most patients with pelvic discontinuity, the acetabular component is large enough to accept an off-the-shelf cage. The types of cage used most often at our institution are malleable cages with iliac and ischial flanges that allow insertion of multiple supplemental screws (Figure 8). Smaller cages are preferred because they provide sufficient room within the cup-cage construct to cement a liner in place. This technique allows delivery of antibiotic-impregnated cement in an otherwise noncemented construct. Moreover, the position of the acetabular component can be slightly adjusted for efficacy when the acetabular liner is cemented.

Figure 8.

Intraoperative photograph depicting our preferred construct using a malleable cage over a highly porous acetabular component, with four screws inserted into the ilium in a transverse pattern and screws inserted through the superior dome of the acetabulum. One to two screws can be placed through the cage, through the acetabular component, and into the host bone to unitize the construct.

When a highly porous augment is used, it is first secured to the host bone with screws and then unitized to the highly porous cup with bone cement introduced with a syringe (Figure 9). Multiple supplemental screws may be placed in the ilium, ischium, and pubis through the highly porous acetabular component. A benefit of certain highly porous metal acetabular designs is that screw holes can be placed anywhere in the cup with the use of a high-speed burr.

Figure 9.

Intraoperative photograph of the same patient shown in Figure 7 showing unitization of the highly porous acetabular component to the highly porous augment after the addition of bone cement.

Distraction Method

In 2012, Sporer et al[21] described the use of pelvic distraction to manage discontinuity. With this method, pelvic stability is obtained via distraction of the discontinuity by elastic recoil of the pelvis and by fixing the superior and inferior hemipelvis to a highly porous metal cup or augment with screws, thereby unitizing the superior and inferior aspects of the pelvis. Although pelvic stability (including rotational stability) prevents motion across the discontinuity site, it is not necessary for the discontinuity fracture line itself to achieve bony healing. The cup acts as a segmental replacement of the acetabulum, with healing occurring up to the cup (or augments) on the superior and inferior borders of the discontinuity, resulting in a unitized and stable hemipelvis.

With the distraction technique, sequentially larger reamers are used until the anterior-superior and posterior-inferior margins of the acetabulum are engaged. After those acetabular margins are engaged, the discontinuity is distracted with an acetabular component 6 to 8 mm larger than the previously used hemispheric reamer. With the use of a jumbo cup in pelvic discontinuity, distraction of the pelvis occurs by placing the inferior aspect of the highly porous acetabular component against the remaining ischium, then bringing the implant into the desired position (Figure 10). This distraction creates an initial press fit, and multiple supplemental screws are placed in the ilium and ischium. In patients with severe bone defects, the reamer may not fully engage these specific regions of the acetabulum. In these patients, porous tantalum augments may be used to fill any large defects. After the augments are secured to the host bone with screws, the acetabular component is impacted into place, and polymethyl methacrylate cement is used to fix the augment-cup interface. Bone grafts are used to fill any remaining cavitary defects.

Figure 10.

Illustration of the distraction method using a jumbo acetabular component to distract (arrows) a discontinuity by 6 to 8 mm. (Reproduced with permission from the Mayo Foundation for Medical Education and Research, Rochester, MN.)

In our practice, the distraction method is used when there is a stiff discontinuity, and modest distraction can lead to elastic recoil.

Custom Triflange Components

Triflange cups are custom-designed, porous and/or hydroxyapatite-coated, titanium acetabular components with iliac, ischial, and pubic flanges[5] (Figure 11). The flanges allow intimate contact between the implant and the host bone for initial stability while maintaining the hip center in or returning it close to its anatomic location. This rigid fixation construct promotes healing of the discontinuity and biologic fixation of the implant. Primary disadvantages of custom triflange components are the relative complexity of the preoperative design and fabrication process and the cost.

Figure 11.

Illustration of a custom triflange construct with iliac, ischial, and pubic flanges. (Reproduced with permission from the Mayo Foundation for Medical Education and Research, Rochester, MN.)

The process of creating a custom component is initiated with a CT scan of the patient's pelvis using metal subtraction software.[5] A 3D model is then created and reviewed by the surgeon to assess head center and cup orientation. After that, the three flanges are designed to facilitate initial fixation. The first row of iliac flange screw holes typically targets the most inferior structural bone of the ilium. The ischial flange normally has three to seven screw holes to accommodate 6.5-mm acetabular screws and typically rests on the posterior surface of the ischial tuberosity. The pubic flange is generally the smallest and typically does not have screw holes. After the design is finalized, the triflange implant is created, sterilized, and shipped to the surgeon.

The surgical technique involves removing prominent bone with a burr to allow optimal fit of the triflange implant using the custom 3D sterile model as a guide. The acetabular socket is gently reamed to allow a smooth fit. If bone graft is used, the surgeon must take care not to lateralize the component with excessive grafting. The custom triflange construct is rotated into the pelvis under the abductors on the ilium. The triflange implant is fixed to the inferior bone of the ischium and pubis (ie, where bone is poorest and lysis is common), after which the discontinuity is reduced and the proximal screws are placed in the ilium. Initially, cancellous screws are placed to compress the implant to the bone. Subsequently, locking screws are placed in the remaining holes to achieve rigid fixation. Typically, 9 to 13 screws are used with this construct.

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